tonestro - Practice & improve on your wind instrument while having fun
EarMaster - Professional software for ear training and practical music theory on Windows and Mac.
Violin by Trala - Violin by Trala is a music learning app that is designed specifically for Violin users.
Meludia - Listening exercises and to sharpen your ear and music theory skills
Simply Piano - Fast and fun way to learn piano
LenMus - LenMus is a free program for learning music.